The present invention relates to a pipe fitting or coupling for connecting pipes, such as water supply pipes, hot-water supply pipes and the like.
As a prior art, a pipe fitting or coupling for connecting pipes, such as water supply pipes and hot-water supply pipes, is formed of a cylindrical coupling main body and a slit ring provided on an outer circumferential surface of an edge portion of the coupling main body. The edge portion of the coupling main body is inserted into an interior of an edge portion of a pipe to be connected, and a nut, such as a cap nut, is screwed onto a screw portion provided on the slit ring to be tightened, thereby to hold and fix the edge portion of the pipe with the coupling main body and the slit ring.
For example, Japanese Patent Laid-Open Publication (KOKAI) No. 4-262189 discloses a pipe coupling formed of an inner layer for constituting an inner circumferential surface of a coupling main body, an outer layer for constituting an outer circumference surface of the coupling main body, and a slit ring. The inner layer is made of a thermoplastic resin having a heat distortion temperature of 95.degree. C. or higher, such as polyether ether ketone, cross-linking polyethylene and polyphenylene sulfide. The outer layer includes a screw portion on one edge thereof and is made of a thermoplastic resin having a screw torque strength of 300 kg/cm.sup.2 or higher, such as polyether imide, polyphenylene sulfide and polyether sulfone. The slit ring is made of a thermoplastic resin, such as nylon and polyethylene having ductility, so that when a nut is screwed onto the slit ring, the diameter of the slit ring is contracted. The inner layer and the outer layer of the coupling main body, and the slit ring are integrally formed.
However, the pipe coupling disclosed in the above publication is short of shear strength in the screw portion formed on the edge portion of the outer layer or a tip portion of the slit ring of the coupling main body, so that a thermoplastic resin to which reinforcing glass fibers are added has been often used.
Although a modulus of shear elasticity, i.e. shear strength in the screw portion, is improved by the thermoplastic resin containing the glass fibers, impact strength is decreased. Therefore, when pipes are connected, if a pipe coupling is dropped, or tools fall down onto the pipe coupling, the pipe coupling may crack or break. Also, depending on a installation condition of a pipe coupling, the pipe coupling is stepped by people or subjected to shocks after installation, so that the same accident or trouble as mentioned above may take place.
The present invention has been made to obviate the above drawbacks of the prior art.
Accordingly, one object of the invention is to provide a pipe fitting or coupling having excellent heat and chemical resisting properties as well as excellent pressure resisting strength, shear strength and impact strength in screw portions formed on an outer circumferential surface of a coupling main body and a slit ring.
Another object of the invention is to provide the pipe fitting or coupling as stated above, wherein the coupling main body and the slit ring are formed integrally so that the pipe coupling can be easily connected to a pipe and handled easily.
A further object of the invention is to provide the pipe fitting or coupling as stated above, wherein the pipe coupling can be easily and economically manufactured.
Further objects and advantages of the invention will be apparent from the following description of the invention.